From 4c95236a335d8b62aa8dbd587bed6a5f30d8265a Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 29 Sep 2022 11:49:35 +0200 Subject: prandom: make use of smaller types in prandom_u32_max When possible at compile-time, make use of smaller types in prandom_u32_max(), so that we can use smaller batches from random.c, which in turn leads to a 2x or 4x performance boost. This makes a difference, for example, in kfence, which needs a fast stream of small numbers (booleans). At the same time, we use the occasion to update the old documentation on these functions. prandom_u32() and prandom_bytes() have direct replacements now in random.h, while prandom_u32_max() remains useful as a prandom.h function, since it's not cryptographically secure by virtue of not being evenly distributed. Cc: Dominik Brodowski Acked-by: Marco Elver Signed-off-by: Jason A. Donenfeld --- include/linux/prandom.h | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'include/linux/prandom.h') diff --git a/include/linux/prandom.h b/include/linux/prandom.h index deace5fb4e62..78db003bc290 100644 --- a/include/linux/prandom.h +++ b/include/linux/prandom.h @@ -12,11 +12,13 @@ #include #include +/* Deprecated: use get_random_u32 instead. */ static inline u32 prandom_u32(void) { return get_random_u32(); } +/* Deprecated: use get_random_bytes instead. */ static inline void prandom_bytes(void *buf, size_t nbytes) { return get_random_bytes(buf, nbytes); @@ -37,17 +39,20 @@ void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state); * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro) * @ep_ro: right open interval endpoint * - * Returns a pseudo-random number that is in interval [0, ep_ro). Note - * that the result depends on PRNG being well distributed in [0, ~0U] - * u32 space. Here we use maximally equidistributed combined Tausworthe - * generator, that is, prandom_u32(). This is useful when requesting a - * random index of an array containing ep_ro elements, for example. + * Returns a pseudo-random number that is in interval [0, ep_ro). This is + * useful when requesting a random index of an array containing ep_ro elements, + * for example. The result is somewhat biased when ep_ro is not a power of 2, + * so do not use this for cryptographic purposes. * * Returns: pseudo-random number in interval [0, ep_ro) */ static inline u32 prandom_u32_max(u32 ep_ro) { - return (u32)(((u64) prandom_u32() * ep_ro) >> 32); + if (__builtin_constant_p(ep_ro <= 1U << 8) && ep_ro <= 1U << 8) + return (get_random_u8() * ep_ro) >> 8; + if (__builtin_constant_p(ep_ro <= 1U << 16) && ep_ro <= 1U << 16) + return (get_random_u16() * ep_ro) >> 16; + return ((u64)get_random_u32() * ep_ro) >> 32; } /* -- cgit v1.2.3 From de492c83cae0af72de370b9404aacda93dafcad5 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Wed, 5 Oct 2022 17:50:20 +0200 Subject: prandom: remove unused functions With no callers left of prandom_u32() and prandom_bytes(), as well as get_random_int(), remove these deprecated wrappers, in favor of get_random_u32() and get_random_bytes(). Reviewed-by: Greg Kroah-Hartman Reviewed-by: Kees Cook Reviewed-by: Yury Norov Acked-by: Jakub Kicinski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 11 +++++------ include/linux/prandom.h | 12 ------------ include/linux/random.h | 5 ----- 3 files changed, 5 insertions(+), 23 deletions(-) (limited to 'include/linux/prandom.h') diff --git a/drivers/char/random.c b/drivers/char/random.c index 01acf235f263..2fe28eeb2f38 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -97,7 +97,7 @@ MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression"); * Returns whether or not the input pool has been seeded and thus guaranteed * to supply cryptographically secure random numbers. This applies to: the * /dev/urandom device, the get_random_bytes function, and the get_random_{u8, - * u16,u32,u64,int,long} family of functions. + * u16,u32,u64,long} family of functions. * * Returns: true if the input pool has been seeded. * false if the input pool has not been seeded. @@ -161,15 +161,14 @@ EXPORT_SYMBOL(wait_for_random_bytes); * u16 get_random_u16() * u32 get_random_u32() * u64 get_random_u64() - * unsigned int get_random_int() * unsigned long get_random_long() * * These interfaces will return the requested number of random bytes * into the given buffer or as a return value. This is equivalent to - * a read from /dev/urandom. The u8, u16, u32, u64, int, and long - * family of functions may be higher performance for one-off random - * integers, because they do a bit of buffering and do not invoke - * reseeding until the buffer is emptied. + * a read from /dev/urandom. The u8, u16, u32, u64, long family of + * functions may be higher performance for one-off random integers, + * because they do a bit of buffering and do not invoke reseeding + * until the buffer is emptied. * *********************************************************************/ diff --git a/include/linux/prandom.h b/include/linux/prandom.h index 78db003bc290..e0a0759dd09c 100644 --- a/include/linux/prandom.h +++ b/include/linux/prandom.h @@ -12,18 +12,6 @@ #include #include -/* Deprecated: use get_random_u32 instead. */ -static inline u32 prandom_u32(void) -{ - return get_random_u32(); -} - -/* Deprecated: use get_random_bytes instead. */ -static inline void prandom_bytes(void *buf, size_t nbytes) -{ - return get_random_bytes(buf, nbytes); -} - struct rnd_state { __u32 s1, s2, s3, s4; }; diff --git a/include/linux/random.h b/include/linux/random.h index 08322f700cdc..147a5e0d0b8e 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -42,10 +42,6 @@ u8 get_random_u8(void); u16 get_random_u16(void); u32 get_random_u32(void); u64 get_random_u64(void); -static inline unsigned int get_random_int(void) -{ - return get_random_u32(); -} static inline unsigned long get_random_long(void) { #if BITS_PER_LONG == 64 @@ -100,7 +96,6 @@ declare_get_random_var_wait(u8, u8) declare_get_random_var_wait(u16, u16) declare_get_random_var_wait(u32, u32) declare_get_random_var_wait(u64, u32) -declare_get_random_var_wait(int, unsigned int) declare_get_random_var_wait(long, unsigned long) #undef declare_get_random_var -- cgit v1.2.3